It is often necessary or desirable for a person to exercise a particular muscle or group of muscles. For example, when a muscle is damaged, such as through injury or surgery, it is important to exercise the muscle to prevent atrophy and to strengthen the muscle for normal use. Further, people exercise healthy muscles to increase strength and to maintain an active and healthy lifestyle, as well as to improve their appearance. Various routines have been developed to exercise different muscle groups by forcing the muscles to contract and extend under a load, such as by moving a free weight against the force of gravity or by moving a handle whose movement is resisted by an exercise machine.
One such exercise is known as a chest press. An exerciser lies supine on a bench and grasps a barbell above him. The exerciser then pushes the barbell upward, away from his chest, and lowers it down. This exercise can be dangerous as the exerciser may drop the barbell. Further, the exerciser should have a partner to spot him in case he fails to lift the weight and becomes trapped below it. Even if done properly with a partner, this exercise may not permit the user a full range of exercise since the barbell may hit the user's chest before the chest and arm muscles have extended fully. When using free weights, the resistance provided by gravity is constant while the strength of the muscles varies over the range of motion. Consequently, the muscles are not fully loaded at each point over the range. During a chest press, the hands seek to follow a curved path inward as the weight is extended from the chest. This path cannot be followed when using a barbell because the hands are maintained at a fixed distance. This deficiency can be overcome by performing the exercise with dumbbells.
To overcome these difficulties, machines have been developed that simulate the exercise movements of a chest press. In one apparatus marketed by the assignee of the instant application, a user exercises by pushing handles away from his chest while in a sitting position. A seat and backrest are mounted to a frame to position a user. Two arms are rotatably mounted as a unit to the frame. The handles are mounted to the arms. The pivot for the arms is disposed above the seat. A cable operably connects the arms to a weight stack such that when a user pushes on the handles, thereby rotating the arms, the weight stack is lifted and provides resistance to the exercise. The cable may extend over a variable radius cam which alters the distance the weight is displaced for a given amount of handle rotation. In this configuration, the resistance to the movement of the handles can be varied to match the strength curve of the chest muscles. While this apparatus has solved many problems associated with performing a chest press exercise with barbells or dumbbells, it does not permit the user to vary the distance between his hands while performing the exercise.
In order to select the weight to be lifted by the user of a typical variable resistance machine (i.e., the weight resistance to the exercise), the user inserts a pin into a rod, thus engaging a portion of the weights in the stack to a tether such as a cable or belt. To provide precision in selecting this weight resistance, the individual weights in the stack must be of relatively small denomination, such as 10 pounds. Many of these low weight plates are required to provide adequate weight resistance to a stronger user. This adds to the cost of manufacturing the machine. Further, in order to select a weight falling between the increments provided, small, loose weights are commonly placed on top of the stack. These supplemental weights can easily be lost or stolen.
In another apparatus, disclosed in U.S. Pat. No. 5,044,631, an exercise machine is disclosed in which levers are rotatably mounted to a frame above the seated user. Handles are mounted to the levers. Resistance to handle movement is provided by weight plates mounted to the levers. The hinges for the levers are disposed at an angle of 20.degree. with respect to a central vertical midplane, such that the user must move his hands in defined arcs in converging planes as he presses forward on the handles. This apparatus forces the user's hands to be brought together at a preset rate as they are pressed away from the chest, regardless of the user's anatomy. This apparatus does not permit the user to select his own path of motion for the press exercise. Rather, the motion is dictated by the angle of the hinges.
A shoulder exercise apparatus is disclosed in U.S. Pat. No. 4,603,856. In this device, a bench is provided for the user to exercise in a prone or supine position. A shaft extends from a ball and socket joint mounted to the side of the bench, and a handle is slidably mounted to the shaft. Frictional resistance is provided both at the ball and socket joint and at the sliding connection between the handle and the shaft. The user exercises by moving the handle against one or both of these resistances. While providing multiple paths of motion through the range of the ball and socket joint, this machine provides for exercising only one arm at a time, cannot coordinate the motion of two arms, and has the disadvantages associated with frictional resistance such as changing resistance due to heat buildup, and wear. Further, this machine only provides concentric action (i.e., where the muscles contract against a load). No eccentric action (i.e., where muscles extend under a load) is possible with this machine.